Energy from Coal

Coal is odd stuff. It varies so much that sometimes you're not sure that it actually IS coal.

In parts of Yorkshire you can find lumps of sea coal on the beach . At Lyme Regis, where it's in compressed layers, you often find lumps of it washed up by the sea or coming out of the cliffs, uusually described by boffins as "shale". Brown coal from Germany is almost like peat, but it creates a stink when you burn it - it's full of sulphur and other nasties. Anthracite is shiny and black and almost clean when you touch it. And ordinary coal varies a lot- sometimes it even contains fossils. This isn't surprising considering that coal is the crushed remains of prehistoric forests. I found a fossil leaf once on a bit of coal, and there are lots of examples in museums.

Coke is different; it's coal with the dirtier bits removed, made by heating coal in a furnace without letting it burn. This is how they make "smokeless" fuel.

Coal is mainly CARBON. Pencil leads are made of the same stuff, and you probably know that it's called graphite. It burns incredibly cleanly. I knew a guy years ago who had to machine pieces of graphite -he used to take waste lumps home to burn on his fire. It contains an amazing amount of energy and sits there in the grate burning with NO smoke at all, glowing almost white-hot, with a pale blue flame ... in many ways an ideal fuel, unless you have to pay for it.

He said the only fuel to compare with it was old shoes, which surprised me.

Now ... carbon looks like this: the black dots are carbon atoms:

hexagons of carbon atoms joined together in graphite

Coal is similar to this - here's a picture I found many years ago:

proposed coal structure

and here's a close-up of part of it:

proposed coal structure, close-up

You can see this coal contains not only carbon but O and N (oxygen & nitrogen). You often get sulphur, too. This is bad news, because if you burn the coal, the smoke is acidic - and this means acid rain.

Nitrogen and Sulphur oxides (they're called Nox and Sox in the trade) are the reason why many of of older power stations in the UK are being shut down. Almost all of the Nox and Sox is removed before venting to the atmosphere( see below), but EU limits for these pollutants are now much lower than they were twenty years ago. There are many more years' life in these older coal fired power stations, and the health hazards are slim to zero, but the political decision has been made and they will have to be switched off anyway, unless an exemption to the 'Large Combustion Plant Directive' can be negotiated.

Power stations in India, China, and Eastern Europe emit much more Nox and Sox than in the UK. The acidic gases are often vented directly to the atmosphere, with little or no attempt to remove them. The gases, along with soot (known as 'particulates') can cause severe local pollution and there are health problems associated with it.

Finally, a few sums...

Ordinary coal often contains about 2% sulphur by weight. So if you burn 100 tons of coal, you're burning 2 tons of sulphur. Here's what happens:

Sulphur + oxygen -----> sulphur dioxide
2 tons .........2 tons ...........4 tons

Add water and oxygen to the sulphur dioxide, and you've got a little over 6 tons of sulphuric acid going up the smoke stack.

You can stop the acid going up the chimney by absorbing it and then chucking away (or using, if you can find a use for it) the spent absorber. Unfortunately the best absorbers are made from limestone, which means more quarries - big ones. Every 4 tons of sulphur dioxide needs 6 tons of limestone.

In the process you make about 6 tons of Plaster of Paris for every 100 tons of coal. You can fix a few thousand broken legs, and make a lot of plasterboard, but what can you do with the rest?

One suggestion is landfill. This would increase sulphate levels in local streams and ponds (and if nitrogen oxide has been absorbed, nitrate levels). Sulphate and nitrate are not toxic but their levels are monitored carefully by the water authorities since an excess can affect the flora & fauna in streams.

So far we've only looked at acid rain, but there's another issue - the much-quoted "greenhouse" effect.

When you burn 100 tons of coal you form about 360 tons of carbon dioxide, all of which goes up the chimney.

The 'establishment' view is that this is affecting our climate.

I have looked through the literature for evidence for this for around thirty years, and found none. Water vapour in any case is the main greenhouse gas, being responsible for around 95% of greenhouse effects. Most chemists and physicists are aware of this, and it is not disputed.

The historical data show that increases in carbon dioxide are generally preceded by a temperature rise. My guess is that this is probably caused by variations in solar activity.

Unfortunately the issue is highly politicised, and when this happens, objectivity goes out of the window.

If you read any blogs / opinions / press releases, therefore, particularly by agencies run or influenced by government (BBC, Royal Society, Met. Office, environmental groups, etc), do so with the utmost caution. Most of the comments you will read have been written or edited by powerful people with their own agendas.

It is interesting that many countries have refused to limit their carbon dioxide emissions, including the U.S.A.

The amount of water vapour in the earth's atmosphere, since our planet is largely covered by ocean, does not vary significantly from year to year. It varies locally from day to day, of course, depending on the weather.

Finally - how much coal is burned in UK power stations?

According to government statistics, about 50 million metric tons a year. (# see footnote)

That's 50,000,000 tonnes, or about a million tons a week.

You can work out the sulphur dioxide, sulphuric acid and carbon dioxide for yourself.

Humans breathe out carbon dioxide, too .... we could even do some sums to see if we give out more than the power stations - but that'll have to be done at another time.

Nigel Deacon / Habitat 21; tidied up and updated on 27 Feb 2013

# footnote
- this piece was originally written in 1996. The figures for 2007, according to Digest of UK Energy Statistics (DUKES 2009) were: UK production 16M tonnes, imports 43M, stock change 3M, total 63M, of which: 52M tonnes were used for electricity, 6M for coke manufacture and 1M for blast furnaces.

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